Preselection tuning system



Aug. 5, 1941. P. F. e. HOLST PRESELEC TION TUNING SYSTEM Filed June 18, 1938 MY Q ZZZ-22:22::

attorney Patented Aug. 5, 1941 UNHTED STATES PRESELECTION TUNING SYSTEM Paul F. G. Holst, Oaklyn, N. J., assignor to Radio Corporation of America, a corporation of Del- The present invention relates to preselection tuning systems for radio receiving apparatus and the like, wherein a reversible electric motor connected with the tuning shaft is caused to stop the tuning operation at any one of a plurality of diiierent adjustable tuning positions.

More particularly, the present invention relates to a tuning system of the type above referred to, wherein the motor is energized through v a pair of reversing discs or contact segments rotatable with the tuning shaft and having a narrow insulator or gap between the contact segments, which in the stopping positions is brought into alignment with any one of a series of contacts connected with selector switches through which the motor is energized.

It is an object of the present invention to provide an improved circuit for a motor tuning system of the type referred to wherein the adjustment of the selector contacts for the various stopping positions may be facilitated.

It is a further object of the present invention to provide an improved indicating circuit in connection with the tuning dial illuminating means of a radio receiver provided with reversible motor tuning means, whereby the selected stopping positions of the tuning means may be indicated visually to facilitate the initial tuning set-up for preselection tuning.

It is also an object of the present invention to provide an improved preselection motor tuning system for radio receiving apparatus and the like having a plurality of signal or station selector means which may easily and accurately be adjusted to tune in selected signals or broadcasting stations, by visual indicating means associated with a manual tuning dial.

It is a still further object of the present invention to provide an improved motor tuning circuit in connection with a tuning indicator dial and pilot lamp, whereby the latter may be utilized for dial illumination during manual tuning as well as during electric or preselection motor tuning, and may also be used in circuit with the motor tuning means for indicating each of the various tuning adjustments for a series of preselection tuning positions of the tuning element.

The invention will be further understood from the following description, when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claim.

Referring to the drawing, the tuning element of a radio receiver system is represented by the three-gang variable tuning capacitor 5 having a tuning control shaft 6, connected through a shaft 1 with a drum 8. A reversible tuning motor 9 having reversing windings Hi and H and a main r 1 operating winding [2 is connected with the drum 8 for driving the tuning shaft 6, through a reduction gearing I3 and a cord drive M between a tuning control shaft I5 with the drum 8. The motor armature I8 is movable axially forward when the motor is energized, to cause a crank arm l9 to engage and drive a star-whee1 28 forming part of the gearing.

The connection between the motor and the gearing provided by the crank arm and starwheel l92l is desirable in order that the motor load may be disconnected from the tuning control shaft [5 when manually tuning the system by means of the tuning knob indicated at 22, since thereby only the gear train l3 is connected with the tuning control shaft l5 and does not appreciably load it.

Manual tuning is accomplished by rotating the control shaft I 5 and the drum 8 through the cord drive I l. Tuning indication is provided by a suitable dial 24 having indicator scales 25 thereon, over which a suitable tuning indicator 26 is moved in response to the tuning adjustment of the receiver. In thepresent example, the tuning indicator is carried by a cord drive 28 which is also connected with the drum 8 as indicated.

In preselection motor tuning, the tuning control shaft of the apparatus is driven by the electric motor 9 which is caused to be de-energized and to stop the tuning operation when the tuning control shaft has been moved to various positions corresponding to desired signals or broadcasting stations to be received. In the present system, the motor drives the tuning shaft from one preselected tuning position directly to the next preselected position without the neces sity of operating a reversing switch at the end of the tuning range, and it is therefore of the homing type.

In this type of tuning, a pair of insulated reversing segments or discs indicated at 30 and 3! are caused to rotate with the tuning shaft 6, being connected therewith through a shaft 32. Each segment covers substantially degrees of rotation, and the segments are separated by a relatively narrow insulator indicated at 33. The segments 30 and 3| are connected, respectively, with the motor reversing windings I0 and H through control leads indicated at 34. The motor is energized from a suitable source of low voltage alternating current such as the secondary winding 35, on the power transformer 36 of the receiver, one side of the secondary being connected through a lead 31 with the main winding [2 and the other side of the supply source being connected through a lead 38 with push button station selector switches 49-44. The switches referred to apply operating current to selector contacts 45-49 which engage the reversing discs or segments 30 and 3| at Various angular positions with respect to the insulator 33.

Current supplied from the secondary 35 through the lead 38 is applied to one of the contacts 4549 selectively and causes the motor to be energized through one or the other of the reversing windings l and II and the main winding l2 until the motor moves the tuning mechanism and the reversing device to bring the insulator 33 into engagement with the selector contact. The motor circuit is then interrupted and the tuning operation is stopped. The insulator 33 is only slightly wider than the contact with which it engages, so that the tuning device is stopped in an accurately adjusted position by the motor means. In case of over-travel, the connection to the reversing segments 30 and 3| is such that the motor tends to move the tuning element to return the insulator 33 to a position under the circuit contact. One of the reversing leads is grounded, as indicated at 5|, and the other lead is connected through a capacitor 52 to a lead 53 which may be extended to other portions of the receiving system to provide silencing of the receiver during the tuning operation by the motor means.

It will be noted that the selector switches are of the single pole double throw type comprising a movable contact 54 and two fixed contacts 55 and 56. Selector switch 39 is a two pole, double throw switch having a grounded movable contact 51, movable between contacts 58 and 59,'and a contact 60 movable between contacts 5| and 62.

It will be noted that the selector switches are normally closed, as shown, to provide connection between the movable contacts 54am thefixed contacts 55 and between the contacts 69 and 6| of the switch 39. This provides a series connection from the supply lead 39 for the motor through the series of switches to the contact arm 54 of the switch 44. The remaining fixed'contacts 56, of the selector switches, are each con-' nected with one of the selector contacts 45-49 on the motor reversing discs, or commutator, whereby when any one of the selector switches 4944 is actuated, the series circuit is interrupted and the motor circuit is completed from the lead 38 to a selected one of the selector contacts 4549. In the present example, the switch 42 is closed to energize the selector contact 41 and, in the position shown, the motor has operated the tuning control to move the insulator 33 under the contact 47 and open the motor circuit;

Additional selector switches and selector contacts may be provided in a similar manner and included in the series for as many broadcasting stations or separately selectable signals as may be desired. It is the usual practice to provide at least six to eight tuning buttons, although in the present example, only five are shown,

The dial is provided with at least one pilot lamp for illuminating the dial as indicated at 65. The lamp is energized from the cathode heating or filament supply winding 66 on the power transformer through supply leads 6! and 68, the latter being connected directly with the winding 66 which is grounded, and the lead 6! being connected with the contact 62 and the contact 56 of the switch 39, as shown. With the switch 39 in the normal open position shown, the contact 51 is grounded as indicated at 69 to complete the indicator lamp circuit to the supply winding 66. The dial is, therefore, illuminated throughout the motor tuning operation.

In this position of the switch 39, the contacts 60 and 6! are closed to energize the motor select-or buttons and the motor circuit from the lead 38.

When the switch 39 is operated to close the contacts 51 and 59 and the contacts 69 and 62, the series push button switch circuit is grounded at 69 through a lead 16 from the last selector switch 44 in the series, and the input end of the selector series circuit is connected to the lead 61 by closure of the contacts 60 and 62.

This last switching operation opens the motor supply circuit with the lead 38 and connects the push button selector switch series circuit with the dial tuning indicator lamp circuit so that the lamp is energized from the secondary winding 66 through lead 68, the lead 61, the contacts 69 and 62, thence through the series contact circuit of each selector switch to the lead 19, through the contacts 51. and 59 to ground 69. and returning to the grounded side of the secondary 66.

The switch 39 is designated as the dial tuning button or switch in the receiver and when depressed provides for manual tuning, since the motor circuit is open, and if none of the selector buttons are depressed, the dial lamp remains on for all positions of manual tuning.

If the dial tuning switch 39 is held closed While a selector switch button is depressed, as, for example, the button 42, the pilot lamp series circuit to ground 69 through the selector switch series circuit is interrupted and is then completed through the contacts 54 and 56 of the switch 42, the contact 41 and either one or the other of the selector disc segments 30 or 3|, one of the leads 34 and through both motor windings Ill and II, in one case, or directly to ground 5!,in the other, depending upon which segment of the commutator device engages the contact'selector by the selector circuit and back through ground to the source 66.

With this circuit arrangement it will be seen that the dial lamp will be de-energized when a selector contact, such as the contact 41, connected in circuit by the actuated or closed selector switch, such as the switch 42, is accurately centered on the insulator segment 33 between the reversing discs 393 I. This circuit arrangement may, therefore, be utilized to adjust the contacts 45-49, inclusive, for setting up the desired preselection stopping positions for the tuning system for motor operation. In each adjustment the pilot lamp provides visual indication of the positioning of each selector contact.

The procedure in setting up the desired position for the various preselected signals or broadcasting stations to be received is simplified by the system shown. The dial tuning switch 39 is closed and a desired signal is tuned in by operating the tuning control system manually. When the signal is exactly tuned in manually, the desired selector button for that particular signal, or broadcasting station, is depressed while the dial tuning switch remains closed, and the selector contact is then adjusted until it lies exactly over the insulator 33, which position is visually indicated by the dial lamp becoming de-energized. If the chosen contact being adand while maintaining the dial tuning switch 39 closed. The selector contact for that switc is then moved until it lies over the insulator 33 and the pilot lamp goes out. This operation is then repeated-for the other selector buttons until the desired number, or all, of the selector buttons are utilized for a serie of preselected broadcasting stations to be tuned in automatically by the motor tuning means.

It will be seen that when the switch 39 is in the open or push button tuning position shown, the motor circuit may be energized through each of the selector buttons, and the motor tuning system will then operate to tune in each of the selected stations which have been set up, as the various selector switches are closed.

The circuit arrangement between the motor and the pilot lamp circuits is such that when the dial tuning switch 39 is in the open position shown, the motor selector switch series circuit is energized from the motor supply source 35 through the lead 38, and when the dial tuning switch 39 is closed, the said series circuit is energized from the pilot lamp source 65 in series with the pilot lamp through the leads 61 and 68. The ground return circuit for the pilot lamp is then completed through the motor circuit which is grounded at the motor and includes the commutator device as an open circuiting means. While the pilot lamp circuit draws very low current, insufficient to operate the motor, the drop in potential through the windings It and H is sufficient to cause the pilot lamp to dim slightly when the segment 3| is in contact with a selected contact, so that, by observing the degree of illuminationof the pilot lamp when adjusting the selected contact, it may be determined in which direction to move the contact to center the contact being adjusted on the insulator 33.

While the pilot lamp circuit and the motor circuit are grounded in the present system, whereby the radio chassis provides a common circuit connection, any other common circuit connection may be provided between the supply source 66 for the pilot lamp and the motor circuit at the motor. The circuit arrangement is such that the motor circuit, including the station selector elements 4944 and 4559, may be energized directly from, its operating source 34 through the selector switch contacts 6t6l and, alternatively, the said motor circuit may be energized from the pilot lamp source 66 through the pilot lamp 65 and the contacts B062. In the first position of the switch 39 the pilot lamp circuit is also directly energized from its source 66, through the contacts 5158. The selector switches 40-44 and the selector contacts 4-5-49 in conjunction with the insulator 33 provide a common means for opening the motor circuit when tuning and for opening the pilot lamp circuit when adjusting the tuning system, whereby visual indication of the contact adjustment is provided by the dial-illuminating mean or pilot lamp.

I claim as my invention:

In a motor tuning system for a radio receiver, the combination of a motor control circuit having an operating winding, a pilot lamp circuit, means for energizing said circuits independently one of another, means for selectively deenergizing said circuits in preselected tuning positions of said system, said deenergizing means further including controlling contact elements connected to said winding, means providing a potential source connected in the pilot lamp circuit and to one of said contact elements, said elements having an insulator element therebetween and selector contacts adjustable in connection with and relative to said contact elements to a position on said insulator element and for including said wirfiling, in the pilot lamp circuit when said contacts engage one of said contact elements and for excluding said winding from the pilot lamp circuit when said contacts engage the other of said contact elements, whereby the pilot lamp circuit is deenergized when said contacts are in engagement with the insulator element and energized in differing degrees when shifted therefrom to the one or the other of said contact elements by reason of the potential drop in said winding.

PAUL F. G. I-IOLST. 

